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Acknowledgements Ground: Geomagnetic field data are provided partly through INTERMAGNET by British Geological Survey, Danish Meteorological Institute, Ecole et Observatoire des Sciences de la Terre, Finnish Meteorological Institute, Finnish Academy of Science, Geological Survey of Canada, Geological Survey of Sweden, Geoscience Australia, Institute of Geological and Nuclear Sciences, Institute of Solar- Terrestrial Physics at Irkutsk, The Irish Meteorological Service, Leirvogur geomagnetic station, Lviv Centre of Institute of Space Research, National Institute of Information and Communications Technology, Polish Academy of Sciences, Tromsoe Geophysical Observatory in Norway, and United States Geological Survey. Cutlass HF data and its interpretation is provided by Mark Lester at Leicester University. Satellites: ACE/Geotail/WIND/Polar/Cluster magnetic field data are provided by the ACE/MAG team (PI: N. Ness at Bartol Reseach Institute) through the ACE Science Center, Geotail/MGF team (PI: T. Nagai at Tokyo Institute of Technology) through ISAS/Geotail page, WIND/MFI team (PI: R. Lepping at NASA/GSFC) through NASA/WIND page, Polar/MFE team (PI: C.T. Russell at IGPP), and Cluster/FGM team (PI: A. Balogh at Imperial College) through Cluster data center. Shock arrival timing detected by Cluster is identified by T. Horbury at Imperial College. The Cluster and Polar particle data for shock identification are provided by Cluster CIS team (PI: H. Reme at CESR) and Polar HYDRO team (PI: J. Scudder at Univ. Iowa) through NASA CDAweb. DMSP convection data is provided by Center for Space Sciences at the University of Texas at Dallas and the US Air Force. GOES satellite project is managed by NOAA, and the data is prepared by A. Newman, LANL satellite project is managed by Los-Alamos National Laboratory, and IMAGE project is supported by NASA.

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Outline * Focus on the initial 6 minutes of the Halloween magnetic storm starting on 29 October 2003 (sudden commencement at 0611 UT). * Observed three onsets of strong ionospheric westward electrojet (2000~4000 nT) in the inner magnetosphere region. (1) Clear substorm onset in the evening-midnight sector staring at 0612 UT, expanding poleward. (2) Substorm-like westward electrojet in the morning sector starting at 0612~0613 UT (rather that cusp-related activity), expanding west. (3) The strongest activity (~4000 nT) in post-midnight sector started where and when the above two expanding activities met each other. * Gather as much data as possible to demonstrate the development.

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Summary (part 3) (3) 06:17 UT A localized sharp development (3000 nT / 2 min ∆B) only at 01 LT (IQA station) together with spiky increase of B by GOES-12 at 01 LT. The onset is when and where two previous activities met at high-latitude midnight. * High and sharp activity + localized + unusual spike at GOES  Difficult to understand. One possible scenario (speculation): a part of the dayside J// system is detached and swept tailward, briefly passing very close to the substorm current system, and that this passage triggered the third activity?